A typical example of a conventional ear thermometer will be explained with reference to FIGS. 15 and 16. FIG. 15 is a circuit block diagram illustrating an operation principle of the conventional ear thermometer and FIG. 16 is a vertical section of a temperature sensing part of the conventional ear thermometer. As illustrated in FIG. 15, a probe 10 of the typical conventional ear thermometer employs a thermopile 11. Generally, the thermopile produces a potential difference depending on a temperature difference between a cold junction and a hot junction (the Seebeck effect). Using the thermopile as a temperature measuring probe needs a room temperature (ambient temperature) compensation like a thermocouple. For this, the conventional ear thermometer employs a thermistor 12.
If the temperature of a measuring object is equal to a cold junction temperature of the thermopile 11, an output from the probe 10 is zero (zero point). On the other hand, if the temperature of the measuring object is higher than the cold junction temperature of the thermopile 11, an output from the probe 10 becomes nonlinearly larger.
When using the probe 10 to measure a body temperature, an output from the probe 10 is weak. Accordingly, the output from the probe 10 is amplified by a signal amplifier 13 to a signal processing possible level. A linearizer 14a linearizes a nonlinear output. An output from the thermistor 12 is also nonlinear, and therefore, is linearized by a linearizer 14b. 
In a state in which an ambient temperature is stable, the temperature of the thermistor 12 and the cold junction temperature of the thermopile 11 are equal to each other. The signal formed by linearizing the output from the probe 10 indicates a difference between the temperature of the thermistor 12 and the temperature of the measuring object. Accordingly, the signal formed by linearizing the output from the probe 10 is corrected by an emissivity corrector 15, the corrected signal and the signal formed by linearizing the output from the thermistor 12 are compensated by an adder 16 for a room temperature or a cold junction temperature, and the compensated signal is compensated by a temperature converter 17 for an ambient temperature, thereby providing the temperature of the measuring object, which is displayed on a display 18.
The thermopile involves a large variation in sensitivity due to individual differences, and therefore, provides a different output voltage with respect to a given temperature difference. Accordingly, a probe employing the thermopile must carry out an individual sensitivity adjustment (calibration work). An infrared absorbing film of the thermopile (a part where the infrared absorbing film and hot junction are integrated, refer to 116 of FIG. 16) absorbs infrared rays from a measuring object and increases the temperature thereof. A package of the thermopile also radiates infrared rays to the infrared absorbing film. In normal use, the package is considered to have the same temperature as a heat sink (heat absorbing part) of the thermopile. If an external factor applies a sudden temperature change, a head of the package and the heat sink of the thermopile produce a temperature difference to transiently destabilize the output of the probe.
For this, as illustrated in FIG. 16, to make a temperature change be uniformly and gently applied to the probe 10, the thermopile 110 is arranged inside a metal (for example, aluminum) holder 111 having a good heat conductivity. In addition, there is arranged a cover 114 to surround the same with an air layer 112 and resin 113 serving as heat insulating materials. In front of the thermopile 110, there is arranged a metal pipe 115 to reduce the influence of heat radiation from the measuring object. The metal pipe 115 is plated with gold to reduce an emissivity and function as a waveguide. As a cold junction temperature compensating sensor, a semiconductor, a thermistor, or the like is employed. The thermistor is low in manufacturing cost and precise, and therefore, is generally used.
If thermal bonding between the thermopile cold junction and the thermistor is bad, a temperature difference occurs to prevent a correct measurement. The thermistor (not illustrated) and thermopile 110 are arranged in the same package, to improve thermal bonding between the heat sink of the thermopile cold junction and the thermistor. Even thermistors based on the same standard have different B-constants (the B-constant representing the magnitude of a resistance change obtained from temperatures at optional two points on a resistance-temperature characteristic curve), and therefore, it is difficult for the thermistor to keep accuracy for a wide range of ambient temperatures. For example, for a thermistor of an electronic thermometer used to measure the temperature of a human body in the range of 34 to 43° C., the thermistor is required to keep an accuracy only for the range of 8° C. If the thermopile must cover an ambient temperature range of 5 to 40° C., the thermistor must be accurate for the range of 35° C. (40−5=35).
According to the structure of the probe 10 illustrated in FIG. 16, an increasing ambient temperature produces a temperature difference between the thermopile 110 and a front end part of the probe 10, so that the temperature measuring part becomes to have a higher temperature than the thermopile 110, to cause a positive-direction error. A decreasing ambient temperature produces a temperature difference between the thermopile 110 and a front end part of the sensor, so that the temperature measuring part becomes to have a lower temperature than the thermopile 110, to cause a negative-direction error. To reduce the error, the thermopile 110 is surrounded with the cover 114 to reduce the influence of a temperature change. Enlarging the metal holder 111 is limited by the measuring object. To cope with the error caused by an ambient temperature change, a rate of change per unit time of the thermistor in the thermopile package is calculated to correct a probe output and reduce the error.
In connection with this, the applicant of the present invention has proposed in a preceding patent application (refer to Patent Document 1) an ear thermometer that eliminates the influence of an ambient temperature change of a short time and causes no error due to the ambient temperature change.
The ear thermometer according to Patent Document 1 has a probe that includes a first heat insulating member made of resin, a second high heat insulating member made of resin connected to a front end part of the first heat insulating member, a protection cover to cover the first heat insulating member and second high heat insulating member, a thermistor lead thin line embedded in the first heat insulating member and second high heat insulating member, and an ultrafast response thermistor arranged substantially at the center of a front return part of the thermistor lead thin line.
According to the invention of Patent Document 1, a temperature range in which the thermistor must keep accuracy is only a body temperature range of a measuring object. Unlike the conventional ear thermometer employing the thermopile, the thermistor is not required to keep a measuring accuracy for an entire measuring ambient temperature range. As a result, the probe according to the invention of the patent application is not influenced by a change in an ambient temperature (a temperature change of a short time).
The ear thermometer according to Patent Document 1, however, has problems of hardly being miniaturized, consuming large power, involving a complicated circuit, and partly needing expensive parts to increase a total cost.
The ear thermometer according to Patent Document 1 is appropriate for once measuring a body temperature in a short period of time, but it is inappropriate for continuously measuring body temperatures for a long period of time. Under a special using condition, for example, when measuring the body temperature of a patient during his/her surgery, a sufficient time is available in a preparatory stage before the surgery. Namely, if a warm-up time of certain extent (about 10 minutes) is allowed, if a large relative temperature and a quick temperature change are ignorable (if sensing a temperature change of 1° C. for 10 minutes at the maximum is sufficient), if continuous measurement is needed, and if ambient temperature is relatively stable, the ear thermometer according to Patent Document 1 is expensive and is inappropriate.
To obtain an ear thermometer that is capable of continuously measuring the temperature of a measuring object for a long period of time and is inexpensive and disposable, the applicant of the present invention has proposed in the succeeding patent application (refer to Patent Document 2) an ear thermometer having a measuring apparatus and a probe that is connected to the measuring apparatus and includes a probe body and a temperature measuring part joined with the probe body. The probe body is substantially formed in an L-shaped cylinder, a first end thereof is connected through a cable to the measuring apparatus, and a second end thereof is connected to the temperature measuring part. The temperature measuring part includes a flange joined with the probe body and a front end part extending from the flange. Inside the front end part, a sensor mirror is fitted. The sensor mirror includes a cylindrical holder with an internal concave reflection face, a joint shaft extending from the back of the cylindrical holder, a temperature measuring first sensor and a correcting second sensor supported with lead wires in a front space of the cylindrical holder, and a protection cover covering a front face of the cylindrical holder. The lead wires supporting the first and second sensors are passed through the temperature measuring part and probe body and are electrically connected to the cable.
In the ear thermometer according to Patent Document 2, a thermistor used for the probe must secure an accuracy only for a temperature range in which the body temperature of a measuring object varies. Unlike the conventional ear thermometer using a thermopile, the thermistor is not required to secure a measurement accuracy for a whole range of measurement ambient temperatures. Under a relatively stable ambient temperature, it is possible to achieve continuous measurement for a long period of time. With a simplified temperature measuring circuit, simplified temperature calibration, miniaturized probe, and simplified assembling work for mass production, this ear thermometer is compact and inexpensive. Accordingly, the ear thermometer according to Patent Document 2 is disposable, is stably and surely attachable to the ear of a measuring object, and is optimum for, in particular, measuring the body temperature of a patient during his/her surgery.
The ear thermometer according to Patent Document 2, however, is configured to support the first and second sensors with the lead wires in the sensor mirror, and therefore, the work to solder the sensors and lead wires together and the work to arrange the sensors in the sensor mirror need a high skill and a long time. Accordingly, this ear thermometer is unsuitable for mass production.
Conventional ear thermometers have the problem that their measuring apparatuses are large in scale, and therefore, it is required to reduce the sizes thereof.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2006-250883    Patent Document 2: Japanese Unexamined Patent Application Publication No. 2007-111363